Pleiotropic drug resistance is characterized by alterations in cell membrane properties. It has been shown that certain chemotherapeutic agents exert antineoplastic effect at the level of membrane. Cyclosporine A (CsA) partitions into phospholipid vesicles and interferes with plasma membrane phospholipid metabolism. It has also been shown to decrease the motional freedom of membrane lipids and to depolarize plasma membrane potentials in murine lymphoctyes. The overall aim of this proposal is to understand the effects of CsA on signal transduction pathway using both neoplastic (sensitive and pleiotropic drug resistant) and normal T and EBV-induced B cell lines. The specific aims of the study are: (1) To compare plasma membrane potentials in sensitive T and B leukemia cell lines and their corresponding drug resistant sublines, and in T and B cells lines derived from normal lymphocytes. The membrane potentials will be studied with DiOC5 dye using FACS. (2) To examine the effect of CsA on the generation of inositol trisphosphate in resistant and sensitive leukemic cell lines and T and B cell lines derived from normal lymphocytes. (3) To study the in vitro direct effect of CsA on the activation and translocation of protein kinase C (PKC) in tumor and normal lymphocyte-derived T and B cells lines. Studies will also be done to examine regulatory role of CsA on PMA-induced activation and translocation will be measured by immunoprecipitation and indirect immunofluorescence, using an alloantibody against PKC. (4) To examine the effect of CsA on membrane phosphorylation of P- 180. The studied would help in the understanding of the mechanisms of CsA on the early steps of lymphocyte activation and the mechanisms by which CsA corrects the pleiotropic drug resistance in neoplastic cells.